Airborne isokinetic sampler

ABSTRACT

A lightweight airborne isokinetic sampler employing a sampling head mounted on a track and connected by flexible hose to the air-moving and controlling equipment located within the aircraft. Flow of air is controlled by a coaxial valve and a bleed-in valve. A pitot tube is used to measure air flow.

o i United States Patent 1 [111 3,707,869 Raynor 1 Jan. 2, 1973 [s41AIRBORNE ISOKINETIC SAMPLER 2,645,941 7/1953 Reid ..73/l70 R x 3,059,47010/1962 Baldwin et al. ..73/l70 R [75] Invent Manmvme' 3,309,518 3/1967Weiss ..73/28 x [73] Assignee: The United States of America asrepresented by the United States Primary Examiner-Richard C, QueisserAtomic Energy Commission Assistant Examiner-C. E. Snee, Ill [22] Filed:June 9, 1971 Attorney-Roland A. Anderson [2!] Appl. No.: 151,402 [57]ABSTRACT A lightweight airborne isokinetic sampler employing a [52] US.Cl. ..73/28, 73/4215 R sampling head mounted on a track and connected by[51] Int. Cl. ..G0ln 1/24, B0ld 46/00 flexible hose, to the air-movingand controlling equip- 0f u 170 421-5 421-5 "3 ment located'within theaircraft. Flow of air is con- 244/1 R trolled by a coaxial valve and ableed-in valve. A pitot tube is used to measure air flow. [56]References Cited 3 Claims, 2 Drawing Figures UNITED STATES PATENTS4/1949 Black ..73/28 X AIRBORNE ISOKINETIC SAMPLER SOURCE OF THEINVENTION BACKGROUND OF THE INVENTION During recent years, there hasbeen increasing interest in the condition of our atmosphere, especiallyas to the presence of. polluting products being discharged by powerplants, industrial complexes, and the like.

One of the problems involved in the control of the discharge of theseproducts is that of monitoring the atmosphere for its particulatecontent in order to know which products should be of real concern. Whilesampling techniques for ground or near ground level :have been developedto an advanced state, the sampling of the atmosphere at altitudes from100 M to about 3 KM 'has remained a difficult problem. For example, thecollection of air samples at any altitude can be readily accomplishedbut'in the situation where the investigator is concerned withparticulate content of the sample, accurate and representative samplesof heterodisperse particulates willnot be obtained unless the collectionis carried out in such a way as not to disturb or alter the kinetics ofthe air flow during collection That is, if the air stream velocity atentrance to a sampler is changed abruptly, thenthe particulates trappedin the sampler will not be truly representative.

Isokinetic sampling has long'been recognizedas the only way to obtainaccurate and representative samples of this type. By isokinetic samplingis meant the taking of sampleswith minimum disturbance of the linesofflow so as to get a true and representative sample of the particulatesuspended. That is, the kinetics of the gas are not disturbed.

Attempts in the past to accomplish this in the range of altitudesmentioned have usually resulted in something less than the mostdesirable results. Balloon.

mounted devices are capable of taking samples of only limited areas, andthis procedure is slow and inefficient, as well as awkward tocarry oninan urban area. Aircraft mounted devices are preferred because of thegreater efficiency, more accurate results as to location,

and greater number of samples which can be obtainedin a given period oftime. Unfortunately, up to now, it has been=difficult, ifnot impossible,to obtain isokinetic sampling from a light aircraft in the altitudesofgreatest interest. Isokinetic sampling systems which have been.

SUMMARY OF THE INVENTION The present invention relates toan isokineticsampler capable of being carried by a light aircraft for obtainingaccurate samples of heterodisperse particulate matter'in the loweratmosphere. The sampler head'is operated in undisturbed air under thewing and is.

drawn into the cabin along a track for changing filters. Abattery-powered, high volume sampler in the cabin serves as the airmoving device. The sampler can draw .as much as 0.72 m minand matchaircraft speeds to 38 ms at standard temperature and pressure, and canbe used for measuring the vertical distribution of a variety ofparticulates including airborne pollens and industrial air pollutantsand for determining their size distribution and composition.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partial schematic of apreferred embodiment of the airborne isokinetic sampling system ofthisinvention;

FIG. 2 illustrates a typical mounting aboard alight aircraft.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, airborneisokinetic sampling system 10 consists of a sampling head 12 connectedby way of a flexible hose 14 to a rigid pipe 16 which leads into a flow,control valve assembly 18, another stretch of rigid pipe 22, and a highvolume sampler 24. A 24 volt.D.C. power pack 28 supplies electricalpower for sampler 24.

Pipe 16 is provided with a pilot tube 32 connected to adifferential'pressure gage 34. As is understood in the art, the end ofpitot tube extending into pipe 16 is turned with its opening'facing theflow of air, the pressure gage 34 showing the static pressure developedinside the pitot tube, indicating with proper calibration the volumerate of flow of'the air within pipe 16 which is the volume rate offlowthrough the whole system.

Flow. control valve assembly 18 is a conventional globevalve with ahand-operated dial 36 for throttling the flow of air through system 10.

Extending from pipe 22 is a bleeder valve assembly 38 with ahand-operated dial 42 for permitting and controlling the amount of airwhich is permitted to be bled into the system, for reasons which willlater be apparent. Valve. assembly 38 also uses a conventional globevalve with an entrance 44 to the air.

Highvolume sampler 24 consists of a rotary blower 46 of any suitabletype driven by a motor 48 ata constant rate. The latter is energizedbybattery power pack 28. Blower 46 discharges to air.

Sampling head 12 consists of a conical entry cone 52 with entry 54 atits narrowest diameter and connected at'its largest diameter to acylindrical filter holder 56. Cone 52 may be threadably or otherwisereadily engaged and disengaged to holder 56, clamping a filter ring 57carrying a circular, flat filter to collect particulate in the airpassing through sampling head l2,and flexible hose l4; Holder 56 ismounted on a slide 58'for a purpose to be described below.

Before completing the description of FIG. 1, reference is made to FIG. 2for the purpose ofindicating how system 10 is mounted for use. There itwill be seen that a frame 62 supportssampling head 12 on light aircraft64.The latter would be typically a single engine single wing aircraftwhich cruises at air speeds of 60 to mph (27 to 38 ms"). Support frame62, which extends out of window 66 of fuselage 67, is supported at itsextended'end by a clamp 68 mounted on'spar 72. A wing mount, using abracket extendingfr'omwing 74, couldalso be used for attachment by clamp68.

Referring to both figures, it is seen that support frame 62 consists ofpair of spaced, parallel rails 76 and 78 supported at their ends byblocks 82 and 84, respectively, and held together by spacer elementssuch as 86a, 86b, 86c, and 86d. Clamp 68 is supported by a block 88mounted on rails 76 and 78. Slide 58 which supports sampler head 12 ismounted for movement along rails 76 and 78. Thus, with frame 62 inplace, sampler head 12 could be retracted when not in use or to replacethe filter. Flexible hose l4 permits this movement.

In order to effect movement of head 12, end blocks 82 and 84 areprovided with pulleys 92 and 94, respectively, on which is wound anendless cable 96. Cable 96 is attached to slide 58 so that the operatorwithin aircraft 64 can retract or extend head 12 by merely rotatingpulley 92 by hand. A replacement plastic window pane 98 with a slideclosure 102 and an opening 104 may be inserted within open window 66 tohelp support one end of frame 62.

In the operation of the apparatus described, with frame 62 mounted on alight aircraft as shown in FIG. 2, a filter is placed within sampler 12which is then moved along tracks 76 and 78 out to its position shown forcollection, by rotating pulley 92. Sampler 24 is then started, andduring the course of operation, it pumps at a constant rate. In order toobtain isokinetic sampling, however, it is necessary to adjust the airflow through sampling system such that the air entering sampling head 52is disturbed as little as possible. That is, the lines of flow of theair immediately in front of opening 54 remain unchanged. By manipulatingvalves 18 and 38, flow is regulated such that gage 34 shows a pressuredifferential corresponding to the preselected flow rate. For aparticular aircraft speed a particular flow rate is required to achieveisokinetic sampling. Valves 18 and 38 must be adjusted to obtain thisreading on gage 34.

If initially gage 34 indicates excessive flow, then valve 38 is openedto reduce the reading on gage 34 to the desired level. If fully openingof valve 38 does not achieve this result, then valve 18 is throttled toreduce the gage reading further.

lf initially gage 34 indicates insufficient flow, valve 18 is openeduntil correct flow is obtained. Should more flow be required with valve18 fully open, then valve 38 is throttled.

It is understood that the end of rails 76 and 78 along with block 82within aircraft 64 may be supported or held in any convenient manner andthat the assembly connected to hose 14 at the remote end from samplinghead 12 is located within fuselage 67 as indicated in FIG. 2. Also, itis readily apparent that divergent section 52 should be aligned axiallywith the axis of motion of the aircraft with entrance 54 facing thedirection of motion. With regard to slide 58, slots in the rear alignedwith rails 76 and 78 are provided to accommodate the supports for spacerelements 860, 86b, etc.

With respect to opening 54, its size is as understood in the art afunction of air speed (i.e., aircraft velocity) and the pumping rateofsampler 24.

It will be seen that the arrangement described herein is useful in thesampling of heterodisperse particulate matter found in the loweratmosphere. The arrangement, being light in weight and simple to manage,can

be used with small aircraft so that the cost of its use is relativelylow. It is also apparent that the simplicity of its construction makesit reliable and easy to maintain.

lclaim:

1. An isokinetic sampling system for air-borne particulate matter foruse with a light aircraft comprising:

a. sampling head means comprising a divergent section having an entrancethereto and a supporting section for receiving flow from said divergentsection;

b. track means extending from the body of said aircraft for supportingsaid sampling head means with said divergent section aligned with theaxis of motion of said aircraft and said entrance facing the directionof motion, said track means having means controlled from within saidaircraft for selectively extending and retracting said sampling headmeans;

c. flexible tube means connected at one end to said supporting sectionfor receiving air entering said divergent section and extending intosaid aircraft;

d. pumping means connected at its suction side to receive air from saidflexible tube means entering and flowing from said divergent section,said pumping means operative at a constant volumetric rate of flow;

e. filter means within said supporting section for removing particulatematter from air passing therethrough; and

f. control means between said flexible tube means and the suction sideof said pumping means for regulating the flow of air entering saidsampling head means to maintain isokinetic flow conditions at theentrance to said divergent section.

2. The sampling system of claim 1 in which said control means includesmeans for indicating volumetric air flow through said system, and valvemeans for altering flow of air into said divergent section.

3. The sampling section of claim 2 in which said valve means includes athrottle valve downstream of said indicating means to adjustablythrottle the flow of air in said system and a bleed valve downstream ofsaid throttle valve at the suction side of said pumping means foradjustably permitting air to enter said system bypassing said systemdownstream of said throttle valve.

1. An isokinetic sampling system for air-borne particulate matter foruse with a light aircraft comprising: a. sampling head means comprisinga divergent section having an entrance thereto and a supporting sectionfor receiving flow from said divergent section; b. track means extendingfrom the body of said aircraft for supporting said sampling head meanswith said divergent section aligned with the axis of motion of saidaircraft and said entrance facing the direction of motion, said trackmeans having means controlled from within said aircraft for selectivelyextending and retracting said sampling head means; c. flexible tubemeans connected at one end to said supporting section for receiving airentering said divergent section and extending into said aircraft; d.pumping means connected at its suction side to receive air from saidflexible tube means entering and flowing from said divergent section,said pumping means operative at a constant volumetric rate of flow; e.filter means within said supporting section for removing particulatematter from air pAssing therethrough; and f. control means between saidflexible tube means and the suction side of said pumping means forregulating the flow of air entering said sampling head means to maintainisokinetic flow conditions at the entrance to said divergent section. 2.The sampling system of claim 1 in which said control means includesmeans for indicating volumetric air flow through said system, and valvemeans for altering flow of air into said divergent section.
 3. Thesampling section of claim 2 in which said valve means includes athrottle valve downstream of said indicating means to adjustablythrottle the flow of air in said system and a bleed valve downstream ofsaid throttle valve at the suction side of said pumping means foradjustably permitting air to enter said system bypassing said systemdownstream of said throttle valve.